using Org.BouncyCastle.Asn1;
using Org.BouncyCastle.Math;

using System;
using System.Collections;

namespace Org.BouncyCastle.Asn1.X509
{
	public class RsaPublicKeyStructure
		: Asn1Encodable
	{
		private BigInteger modulus;
		private BigInteger publicExponent;

		public static RsaPublicKeyStructure GetInstance(
			Asn1TaggedObject	obj,
			bool				explicitly)
		{
			return GetInstance(Asn1Sequence.GetInstance(obj, explicitly));
		}

		public static RsaPublicKeyStructure GetInstance(
			object obj)
		{
			if (obj == null || obj is RsaPublicKeyStructure)
			{
				return (RsaPublicKeyStructure) obj;
			}

			if (obj is Asn1Sequence)
			{
				return new RsaPublicKeyStructure((Asn1Sequence) obj);
			}

			throw new ArgumentException("Invalid RsaPublicKeyStructure: " + obj.GetType().Name);
		}

		public RsaPublicKeyStructure(
			BigInteger	modulus,
			BigInteger	publicExponent)
		{
			if (modulus == null)
				throw new ArgumentNullException("modulus");
			if (publicExponent == null)
				throw new ArgumentNullException("publicExponent");
			if (modulus.SignValue <= 0)
				throw new ArgumentException("Not a valid RSA modulus", "modulus");
			if (publicExponent.SignValue <= 0)
				throw new ArgumentException("Not a valid RSA public exponent", "publicExponent");

			this.modulus = modulus;
			this.publicExponent = publicExponent;
		}

		private RsaPublicKeyStructure(
			Asn1Sequence seq)
		{
			if (seq.Count != 2)
				throw new ArgumentException("Bad sequence size: " + seq.Count);

			// Note: we are accepting technically incorrect (i.e. negative) values here
			modulus = DerInteger.GetInstance(seq[0]).PositiveValue;
			publicExponent = DerInteger.GetInstance(seq[1]).PositiveValue;
		}

		public BigInteger Modulus
		{
			get { return modulus; }
		}

		public BigInteger PublicExponent
		{
			get { return publicExponent; }
		}

		/**
		 * This outputs the key in Pkcs1v2 format.
		 * <pre>
		 *      RSAPublicKey ::= Sequence {
		 *                          modulus Integer, -- n
		 *                          publicExponent Integer, -- e
		 *                      }
		 * </pre>
		 */
		public override Asn1Object ToAsn1Object()
		{
			return new DerSequence(
				new DerInteger(Modulus),
				new DerInteger(PublicExponent));
		}
	}
}
